This invention relates to composite pushrods and more specifically, to polymer matrix composite pushrods.
Overhead valve internal combustion engines typically employ a “valve train” which regulates the motion of valves used to control the flow of combustion and exhaust gases into and out of each engine cylinder. Among the numerous components of such valve trains are “pushrods” which serve, among other components, to convert rotating motion from the rotating camshaft of the engine into linear motion of the individual valves on each cylinder. It has long been recognized that improvements to the valve train can lead to significant improvements in overall engine performance. More particularly, valve train components of increased stiffness, reduced weight and/or improved vibration damping properties have been suggested as possible enhancements to lower engine noise, increase engine speed, increase engine power and improve fuel efficiency, particularly in high performance overhead valve engines.
Pushrods made using polymer matrix composite materials have been proposed as alternatives to traditional metal pushrods. In order to provide sufficient wear of the pushrod at its ends, separate endcaps typically of a harder material, such as a metal, were fitted at both ends.
Male endcaps have been used at the ends of polymer matrix pushrods to prevent failures of the composite rod. However, “brooming” of the ends of the composite rod or tube still could occur due to compression forces on the ends of the pushrods and splitting of the composite tube still could occur if a typical interference fit endcap pin were used.
Female endcaps, i.e., endcaps having a crown and a skirt that fits over the ends of the polymer composite rod, have been proposed to prevent brooming of the ends of the composite rod. Such female endcaps must typically be custom designed and fabricated for these applications. This is because most commercially available endcaps for various rod diameters, tip diameters, and tip designs are male rather than female. Also, adhesive bonds used to hold the female endcaps on the rod are typically less reliable than interference fit.